As an active layer, an oxide active layer, such as indium gallium zinc oxide (IGZO), has carrier mobility, which is 20 to 30 times larger than that of amorphous silicon. This oxide active layer may greatly increase the charge/discharge rate of the TFT to the pixel electrode, improve the response speed of the pixel, and thus achieve more quickly refreshment rate, and therefore is a suitable material for the channel layer in the new generation thin film transistor liquid crystal display (TFT-LCD).
Generally, in an oxide TFT device, source/drain electrodes are contacted with the oxide active layer directly. At both sides of the oxide active layer, there is no PN junction between the oxide active layer and the source/drain electrodes. Thus, holes in the oxide active layer will flow into the source/drain electrodes, or the electrons in the source/drain electrodes will flow into the oxide active layer, which will increase the leakage current between the oxide active layer and the source/drain electrodes, and leads to the phenomenon such as picture blinking, crosstalk, or residual image of the display panel.